


A Foxy Heat

by Canadian_BuckBeaver



Category: Fellswap - Fandom, Undertail - Fandom
Genre: Alternate Universe, Alternate Universe - Undertail (Undertale), Anal Sex, Double Penetration, Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Established Relationship, F/M, FS!Papyrus - Freeform, FS!Sans - Freeform, Gross, Hiding, M/M, Mating Cycles/In Heat, Multi, Multiple Orgasms, Multiple Penetration, Multiple Sex Positions, NSFW, Oral Sex, Original Character(s), Penis In Vagina Sex, Polyamorous Character, Polyamory, Polyamory Big Bang, Post-Traumatic Stress Disorder - PTSD, Riding, Sexy, Sexy Times, Shameless Smut, Sibling Incest, Smut, Undertale Skeletons in Heat, Vaginal Sex, fellswap
Language: English
Status: Completed
Published: 2018-09-03
Updated: 2018-09-03
Packaged: 2019-07-06 07:37:19
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,033
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15881526
Author URL: https://archiveofourown.org/users/Canadian_BuckBeaver/pseuds/Canadian_BuckBeaver
Summary: Alana is acting a little funny today.  She all but ran out the door in the morning and hasn’t been back home since.  Black (SF!Sans) and Slim (SF!Papyrus) are getting worried.  Despite all that they have been through together, this is still Swapfell.  The land where monsters hunger for EXP.  They just need to make sure that she is ok…





	A Foxy Heat

**Author's Note:**

  * For [AlanaRose](https://archiveofourown.org/users/AlanaRose/gifts).



“ALANA?  ALANA? WHERE THE FUCK ARE YOU, ALANA!”  The little FellSwap Sans was stomping around the Waterfall area, screaming at the top of his lungs.  Cupping his hands around his mouth, Black was positively loud enough to wake the dead. His eye lights flashed deep red, searching the dark area for one specific soul.

Slim sighed, shaking his head.  They had been searching for a little over two hours now but to no avail.  Alana’s past had taught her well, if she did not wish to be found, she would not be found.  Simple as that.  His cigarette briefly flared as he took a deep drag, eyes travelling the expanse of the land.  They had already looked all over the rest of the Underground, where on Toriel’s green earth could that girl be?

By the stars, when she said that she wanted to be left alone, she meant it.

* * * * *

Alana already stood out from the other monsters as a monster-human hybrid.  When Slim and Black were first created, Gaster had also fashioned Alana.  For what, they did not know for sure, though his paperwork suggests that he was trying to discover if stress on a soul could cause it to multiply.  Although he did not solve his original hypothesis (he had disappeared before Alana’s soul could be affected anymore from his cruel experiments, luckily), he had created Alana into the delightful creature that she was today.  She almost appeared completely human with a couple, special additions.  Fluffy orange fox ears sprang from underneath her brown hair, twitching and just as useful as a regular fox’s ears, and a glorious orange and white fox tail curled majestically from her rump.  She was one of a kind.

After the disappearance of Gaster, Slim, Black and Alana had decided to stay together.  It would be safer for them, on the off chance that he did reappear and, even if he didn’t, they knew only of each other.  They knew nothing of the outside world or the monsters outside.

Yes…. Better together….

* * * * *

“I CAN’T FIND HER ANYWHERE!” Black spat, stomping up to Slim.  “WHEN SHE SAID THAT SHE WANTED TO BE LEFT ALONE…. WELL, I DIDN’T THINK THAT SHE WOULD BE GONE SO LONG.”  Slim noticed that the tone in his voice changed at the end. Gone was the commanding officer. Here was the concerned friend.

Slim wrapped a comforting arm around him.  “I know, bud. We’ll find her.  She couldn’t have gotten far.”  He scanned the distant horizon, listening and watching.  The flowers waved gently in the artificial breeze, the Floweys were calling out to one another in their signature way…

No sight or sound of her.

“WHAT IF SOMEONE KILLED HER? IF I FAILED TO PROTECT HER…”  Black did not shrug off his brother’s protective arm as he often did.  Instead, he let it rest on his shoulders, allowing it to pull him closer to the black jacket he claimed to hate.  A gloved hand came up, rubbing at his sharpened fangs nervously.

“M’lord, you would have killed anyone who dared put a single hair out of place,” Slim told him, “the other monsters know better than to touch your property.  And, have they tried your patience anyways, I would have helped you hide the dust.”

Black considered what he said before sighing and puffing out his chest.  The familiar title helped stabilize his thoughts.  He was a lord of war, not of fear or uncertainty.  “YOU’RE ABSOLUTELY RIGHT, MUTT.  SHE WEARS THAT COLLAR AROUND HER NECK BECAUSE SHE BELONGS TO ME… US.” he corrected, looking to Slim.

The elder skeleton exhaled smoke, smiling softly at his brother.  Black came off as rough, angry and powerful, but, underneath it all, he truly cared.  He had a hard time showing it sometimes but…  Slim paused in his thoughts, staring at a crack in the cliff.  

The Waterfall had always been full of cracks and niches, little caves that spiralled deeper into the rock. There were countless caves and trails in the rock.  If an unlucky monster wasn’t careful, they could get lost.  “I know where she is.” He said suddenly.  Taking a last inhale of smoke, he extinguished the smoke. Ignoring Black’s questions, he came close to the cliff.  There…

“ORANGE FUR, CAUGHT IN THE ROCKS…” Black whispered, eye lights widening.

Slim grinned.  “Let’s go, little brother.”

* * * * * *

It took a little bit, crawling through the caves and little crevices.  The deeper that they crawled, the darker the cave became.  There were fewer echo flowers here and with the light of the artificial sun or moon couldn’t reach them.  For the skeletons, it didn’t matter.  Their eye lights automatically adjusted the light for them, allowing them to see their way.  Deeper and deeper they travelled, and the only difficulty they faced was Slim trying to fit through some of the smaller areas.

It was truly the best area for a hiding fox.

As they walked they made sure to talk in low, slow voices.  From Alana’s previous experiences and Gaster’s truly monstrous experiments, loud and sudden noises would scare, no, terrify her, possibly causing her to flee or hide.  All their progress of making their way through the caves would be nought.  As it was, they were already scared of scaring her off.  This morning she had been deadset against company on her walk…

But they had no other choice.  What if she was injured or worse?  The two brothers would never forgive themselves if that was the case.

The trail of the cave led to a small opening deep in the cave.  Black entered the area immediately, unafraid of anything that could lurk in the shadows.  His brother was much more careful.  Glancing around, Slim realized that this was a rare part of FellSwap Underground that remained untouched.  Usually caves or caverns similar were used as bases or hidden hunting spots.  Here it was musty, dusted with a slightly musky scent.  Stalagmites dotted the area, the water running from them echoing along the enclosed area…

A terrified hazel eye stared at them from around such a cluster.

“Alana,” Slim whispered quietly, doing his best not to frighten her further.  Black gasped and whirled around, looking to where Slim stared. His eye lights brightened at the sight of her.  Relief flooding through his bones.  She was here, she was safe…

But was she injured?

She squeaked and ducked around the rock.  “Go away,” she moaned, causing the two brothers to startled.  She sounded like she was in pain.  Were they too late?  “You two should not be here.  I told you that I needed to be left alone….”

Slim shook his head. “You know how well I follow orders.” Alana’s eyes widened at that and she giggled.  A small giggle mind you, over before you could blink, but it was a comforting sound.  She just might be ok.  “And besides, you have been gone the entire day.  We were worried about you.”

Alana sighed.  “Has it been so long already?”

“Yes.  The entire day.  Black thought that you were captured or killed.” Slim said, eyeing his brother.  Black was being awfully silent.  His eyes were fixated on her and a small flush was slowly building across her cheekbones.  Slim frowned. He was acting highly out of character.

“I’m… I’m sorry… I’m just…” Alana looked around, looking anywhere but at them.  The air in the cave was thick and uncomfortable, hot and suffocating. Tiny beads of sweat shone on her skin, seen in the faint light. “I wanted to be alone today and… lost track of time…”  She looked highly uncomfortable and antsy, her eyes flitting from side to side.  The smallest whimper escaped her mouth.

Just what exactly was going on?

“Is that it, really?” Slim asked.  He folded his hands across his chest, eyeing her.  She flinched slightly, withdrawing further into the shadows.  Shit.  Not what he wanted.  He tried a different method.  “You know you don’t have to lie to us,” he told her.  “We’ve been together for stars knows how long and much worse shit than anyone else.  You don’t need to hide…”

“IT IS HER HEAT,” Black told him simply, eyes narrowing slightly.

That got Slim’s attention. “What?” he asked.  “I thought that humans…”

“THE SMELL TO THE AIR, THE WAY SHE IS ACTING IS EXACTLY LIKE A MONSTER IN HEAT,” Black said, turning slightly to him.  His eyes were glazed over now, hungry.  “AND SHE IS NOT EXACTLY HUMAN ANYMORE.  NOT AFTER WHAT GASTER DID TO HER.”

Alana flushed a deep red as she yelped, hiding behind the rocks. “Go away!” she said again to them. “I am fine!  I don’t need… I don’t need your help!”

“NOW THAT IS SOMETHING THAT I HIGHLY DOUBT.”  Black was trembling slightly, fighting to keep his instincts under strict control.  “WE ALL KNOW THAT IT TAKES LONGER TO SATISFY A HEAT IF YOU DO NOT HAVE A PARTNER.  THE LONGER IT TAKES, THE MORE YOU RISK YOUR SOUL’S INTEGRITY…”

Alana flinched slightly, bowing her head as if smacked.  Her eyes were slightly fearful but still held that deep, insatiable hunger for them.

“It is nothing that we haven’t done before,” Slim said softly, trying to calm her nerves.  “We don’t mind helping you…”

“IT’S NOT THAT!” Alana spat before covering her mouth and looking away, slightly shamed.  It wasn’t often that she got so emotional.  “It’s not that at all… I just… I don’t want you guys to feel obligated to help me out.  I know that we have done it before…”  Her years in confinement and then in FellSwap had not helped her confidence levels.

“SO THEN YOU SHOULD KNOW THAT IT REALLY IS NO OBLIGATION FOR US TO HELP YOU,” Black told her.  “ALANA… WE CARE ABOUT YOU FOR YOU.  NOT JUST FOR YOUR HEAT.  BUT FOR YOUR HEALTH AND WELLNESS.  WE… WE…. LO…” Black looked like he was gagging.  After all this time he still couldn’t say the words.  Seems like FellSwap was too far trained into his mind.

“We love you, Alana,” Slim said softly.  “This is what we do.  We are a team, always have been.  And, as a team, we help each other…” Slim slowly approached her, placing a hand on her shoulders.  “This is just another situation.  Another problem that we can solve together.  You don’t need to be alone, Alana.  We are here.  For better or worse.”

Shivering, Alana looked up at him.  Fearfully at first before slowly gaining more confidence.  “I… I could use a hand…” she finally admitted, flushing.  “I’ve been trying all day…”

Black wrapped around her back, pulling her back into his arms and holding her tight.  With a small grunt she fell into his waiting lap.  “WELL, IT DOES TAKE A LOT TO REPLACE THE MAGNIFICIENT SANS.” He said, winking at her before gently biting her neck.  Not enough to puncture, but just to leave a gentle bruise.  Her startled gasp was his reward, her eyes widening at the pleasure sparking through her body.

Chuckling, Slim drew close to her.  “You seem surprised, little one.   Perhaps after so long you were expecting your body not to react to us?” his fingers traced under her chin, pulling her face up to see his.

“THAT IS IMPOSSIBLE BROTHER, AND YOU KNOW IT,” Black said, nipping at her earlobe.  “WE ARE IMPRINTED TOO DEEP INTO HER.”

Slim’s fingers ran slowly up her sides, purring softly.  “Good… because she belongs to us.” He told them, his fingers gently clinking against the collar around her throat, the small tag catching in the dim light.  “Always…”  Their magic had begun to form in reaction to her request.  Slim’s pants were glowing with a deep orange, Black’s a violet purple.

Alana gave a startled smile as she felt their rods form, heard their words, her eyes softening.  Good, despite her heat-affected mind, her thoughts were clear.  Seems like their words and little gestures were having the perfect reaction.

Good.  Perhaps they weren’t too late for her.

* * * * *

Alan cried out softly as she came again, cheeks flushed a soft pink, throwing her head back, and giving the boys a perfect look of her gleaming body, her lean sinews.  A makeshift bed of nearby moss, grass and their clothing had been hurriedly tossed together in a haphazard nest, but it didn’t matter.  It was complete heaven.  It might as well be made of the finest linens and softest blankets.

Stroking her skin, they purred encouragingly to her.  This heat, as all first heats were, were bad.  Strong and seemingly never-ending. Already they both had come several times, and yet she demanded, needed, more.  Though there were signs of improvement.  The sweet, musky smell wasn’t as strong, nor did she appear so animalistic.

Perhaps they were finally beginning to sate its hunger.

Panting, Alana looked between the two skeletons.  Her legs were wrapped around the both of their hips, her arms thrown over their necks.  She positively covered in their cum, both her folds and her other hole oozed of it, the orange and purple juices staining her skin like fireworks.  Gripping her waist gently, Slim prepared to move again.

“W-w-wait…” she whispered to them.  Pausing, Black and Slim looked at her carefully.  Had she been hurt?  Was she ok? Hungry?  Thirsty?  “I… I want to try something… if you are willing.” She murmured softly, looking between them.

“THE MAGNIFICENT SANS DOESN’T NOT BACK DOWN FROM A CHALLENGE.” Black confidently said.

Slim nodded in agreement. “Whatever you want, darling…”

Gasping for breath, Alana sighed.  “I’ve… I’ve only seen this position once or twice… so… just… bear with me…” she told them, pulling out of them with a little popping noise.  “Both of you, both on your backs…”

A few moments later, Slim and Black lay on their backs across from one another, the very curves of their pelvises just touching, and legs wrapped around one another.  Slim looked up at the ceiling, trying to slow his soul beat.  Just what exactly did she have planned?

A hazel eye peeked at them quickly.  “Perfect,” Alana whispered.  

“WHAT EXACTLY… HOW IS THIS PERFECT?” Black asked.

A nervous giggle escaped her as she settled next to their pelvises.  “You’ll see very soon, Black.”

Slim opened his mouth, about to ask another question, when a moan escaped instead.  Alana had seized their two cocks in her hand and had started stroking them together.  Sloppy noises were heard as she began to lubricate the two of them with their own mixture of cum and juices. He could feel Black’s erection against his, and Alana’s warm fingers trying to cup them both…

Damn that was different but so good…

Once she was satisfied that they were wet and ready for her, Alana gripped the two of them tight at their base, holding them together.  Carefully positioning them at her entrance, she began to press them inside.

He almost couldn’t hear Alana’s sounds over the moans of his brother and him.  She was so wet and warm and messy… so good and perfect… sliding on them so slow and sweet, being careful not to hurt either of them or herself. Inch by silken inch she pressed on.

Finally.  Finally, she had hilted herself on them.  She had taken them both in her tight little pussy. Slim thought he might just come out of excitement for what she had planned next.

Shivering and gasping, Alana gripped his spine, trying to steady herself.  Black, for once patient, and Slim watched on, waiting for her commands or orders.  This was Alana’s time for pleasure.  Licking her lips, she began to raise herself, rising herself to their very tips, before pressing herself down again.  Riding them both at the same time.

Slim groaned, resting his arms against the ground as to better watch her.  He could feel everything.  Her muscles shivering around him, their combined mess, and his brother’s rod twitching beside him as he felt the same stimulus that he did.  Alana’s little kitten noises as they rubbed against the perfect spots, stretching her out and finding those hidden areas deep inside of her.

By the stars it was wonderful.

“Oh… Oh, we should have done this sooner…isn’t… isn’t that right?” she whispered, leaning forward to Slim, letting Black watch her ass as it rose and fell with her movements.  Slim’s eyes were focused completely on her but he could feel his brother shiver with discreet pleasure.  When he realized that she had asked a question, it was too late.  Alana, gaining more confidence in her abilities and limits, had started to move faster, her cheeks bouncing against the hard bones, their mixture slowly oozing out of her and over them.  Her tail was raised high, also trembling with pleasure.

“Oh, stars, Alana… don’t stop,” Slim pleaded with her, letting his head fall back.  Black mewled in agreement, panting in pleasure.  Although not in heat themselves, the two brothers had been able to push themselves far beyond their normal limits.  They would pay for it tomorrow, but for now, they just didn’t care.

“Don’t… don’t stop, hmm? You must… must be enjoying this as much as I am.” She moaned softly, slamming herself down on them and rocking against them before rising again.  “Do you enjoy feeling me like this?  Do you like me taking control?”

“OH FUCK YES…” Black whispered, tongue lolling between sharpened teeth.

Alana giggled softly before moaning again, feeling their heads brush against her in that perfect way. Despite her dirty talk, she was close too. “Oh stars, come on guys.  Fill me.  Fill me with your hot magic…. I need it.”

As if on command, Black and Slim groaned and came, pumping their hot magic into her.  Strand after strand, they filled her again, until…

Screaming quietly, Alana came again, slamming her body on them, anchoring herself to them.  Broken moans escaped her mouth as they continued to come, filling her with their magic come as she had wished.  “Wow…” she whispered, slowly lowering herself onto Slim’s ribs, still connected to the two of them.  “Wow… that was so good… after… after a nap… can we do that again?”

Two tired groans were her only response.

**Author's Note:**

> Hopefully you guys enjoyed! If you enjoyed what you read, please leave me a kudos or a comment!


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